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Ilia Sharin 21751c0025 docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections

Comprehensive technical documentation covering:
- Hardware: OCS/ECS/AGA custom chip registers, Copper & Blitter deep dives
- Boot sequence: cold boot through startup-sequence
- Binary format: HUNK executable spec, relocation, debug info
- Linking & ABI: .fd files, LVO tables, register calling conventions
- Exec kernel: tasks, interrupts, memory, signals, semaphores
- AmigaDOS: file I/O, FFS/OFS layout, CLI/Shell scripting
- Graphics: planar bitmaps, Copper programming, HAM/EHB modes
- Intuition: screens, windows, IDCMP, BOOPSI
- Devices: trackdisk, SCSI, serial, timer, audio, keyboard
- Libraries: utility, expansion, IFFParse, locale, ARexx
- Networking: bsdsocket API, SANA-II, TCP/IP stack comparison
- Toolchain: GCC, vasm/vlink, SAS/C, NDK, debugging
- Reverse engineering: IDA/Ghidra setup, compiler fingerprints, case studies
- CPU & MMU: 68040/060 emulation libs, PMMU, cache management
- Driver development: SANA-II, Picasso96/RTG, AHI audio

All files include breadcrumb navigation. No local paths or proprietary content.

2026-04-23 12:17:35 -04:00

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← Home · Graphics

Animation — GEL System: BOBs, VSprites, AnimObs

Overview

The GEL (Graphics ELement) system provides high-level animated sprite and bitmap overlay support. It manages VSprites (virtual sprites that can use hardware or software rendering), BOBs (Blitter OBjects — arbitrary-sized bitmaps overlaid on a playfield), and AnimObs (animation objects with sequencing).

VSprite

/* graphics/gels.h — NDK39 */
struct VSprite {
    struct VSprite *NextVSprite;
    struct VSprite *PrevVSprite;
    struct VSprite *DrawPath;
    struct VSprite *ClearPath;
    WORD   OldY, OldX;        /* previous position */
    WORD   Flags;              /* VSPRITE, SAVEBACK, OVERLAY, MUSTDRAW */
    WORD   Y, X;               /* current position */
    WORD   Height;
    WORD   Width;              /* width in words */
    WORD   Depth;
    WORD   MeMask;             /* collision mask */
    WORD   HitMask;
    WORD   *ImageData;         /* sprite image */
    WORD   *BorderLine;        /* collision border */
    WORD   *CollMask;          /* collision mask data */
    WORD   *SprColors;         /* colour table */
    struct Bob *VSBob;         /* if this VSprite backs a BOB */
    BYTE   PlanePick;
    BYTE   PlaneOnOff;
    /* ... */
};

BOB (Blitter Object)

struct Bob {
    WORD   Flags;
    WORD   *SaveBuffer;       /* background save buffer */
    WORD   *ImageShadow;      /* shadow mask for cookie-cut */
    struct Bob *Before;
    struct Bob *After;
    struct VSprite *BobVSprite; /* associated VSprite */
    struct AnimComp *BobComp;   /* if part of animation */
    struct DBufPacket *DBuffer; /* double-buffer packet */
};

Usage Pattern

struct GelsInfo gi;
struct VSprite headVS, tailVS;

/* Initialise GEL system: */
InitGels(&headVS, &tailVS, &gi);
rp->GelsInfo = &gi;

/* Add a VSprite/BOB: */
AddVSprite(&myVSprite, rp);
/* or */
AddBob(&myBob, rp);

/* Each frame: */
SortGList(rp);       /* sort by Y position */
DrawGList(rp, &vp);  /* render all GELs */
WaitTOF();           /* sync to vertical blank */

/* Cleanup: */
RemVSprite(&myVSprite);
/* or */
RemBob(&myBob);

AnimOb — Animation Sequences

struct AnimOb {
    struct AnimOb *NextOb;
    struct AnimOb *PrevOb;
    LONG   Clock;           /* frame counter */
    WORD   AnOldY, AnOldX;
    WORD   AnY, AnX;        /* current position */
    WORD   YVel, XVel;      /* velocity */
    WORD   YAccel, XAccel;  /* acceleration */
    WORD   RingYTrans;      /* ring buffer Y translation */
    WORD   RingXTrans;
    struct AnimComp *HeadComp; /* component chain */
    /* ... */
};

References

NDK39: graphics/gels.h, graphics/gelsinternal.h
ADCD 2.1: InitGels, AddVSprite, AddBob, SortGList, DrawGList
Amiga ROM Kernel Reference Manual: Libraries — GELs chapter

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